The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Is 5mg Mounjaro Not Working for You?
If you're on a 5mg Mounjaro dose and not seeing the weight loss results you expected, you're not alone. Weight loss medication doesn't work the same way for everyone, and dose response varies significantly between individuals. This guide compares Mounjaro and Wegovy to help you understand your options and what to discuss with your prescriber. Remember: 5mg is typically an early maintenance dose — many people require higher doses for optimal results, and your prescriber may recommend escalation based on your response and tolerance.
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Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
Mounjaro vs Wegovy: Mechanism and Trial Data
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. In the SURMOUNT-1 clinical trial, participants on 5mg Mounjaro achieved an average weight loss of approximately 15% body weight over 72 weeks, whilst those on the maximum 15mg dose achieved around 21% loss. The 5mg dose is typically a first maintenance dose — many prescribers escalate after 4 weeks if tolerated.
Wegovy (semaglutide) is a GLP-1 agonist only, activating a single hormone pathway. In the STEP-1 trial, average weight loss at the maximum 2.4mg dose was approximately 15% body weight. Wegovy does not have a dedicated 5mg equivalent — doses progress from 0.25mg to 2.4mg.
- Both require a reduced-calorie diet and increased activity for optimal results
- Clinical trial results show individual variation — some people achieve more, some less
- Mechanism differences may affect tolerability and response in different individuals
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
When to Discuss Dose Changes with Your Prescriber
If you've been on 5mg Mounjaro for at least 4 weeks and haven't seen meaningful progress, your prescriber may recommend dose escalation to 7.5mg or higher, depending on your tolerance and health. Some people respond better at higher doses; others see better results with a longer timeframe on the current dose. Your prescriber will consider factors including side effect tolerance, appetite suppression, blood sugar control (if diabetic), and your baseline weight.
Switching between Mounjaro and Wegovy is also an option — your prescriber can assess which mechanism might suit you better. Both medications require UK prescription and clinical assessment. Use our free BMI calculator above to track your current position, and our GLP-1 weight loss calculator to see projected outcomes at different doses — these tools help clarify what realistic progress looks like for you.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Why might 5mg Mounjaro not be working for me?
Individual response to weight loss medication varies significantly due to genetics, metabolism, baseline weight, diet adherence, activity level, and other health factors. 5mg is often an early maintenance dose — many people require higher doses (10–15mg) for optimal effect. Poor weight loss may also reflect insufficient calorie deficit alongside medication, or individual non-response, which your prescriber can assess.
Should I switch from Mounjaro to Wegovy if 5mg isn't working?
Possibly, but this depends on individual factors. Mounjaro's dual mechanism (GIP + GLP-1) works differently from Wegovy's single GLP-1 mechanism, and some people respond better to one than the other. Before switching, discuss with your prescriber whether dose escalation or longer treatment duration might be better. Any switch requires a new prescription and clinical assessment.
What dose of Wegovy is equivalent to 5mg Mounjaro?
There is no exact equivalent. Approximate rough comparison: 5mg Mounjaro is roughly equivalent to 0.5–1mg Wegovy based on clinical trial data, but these are different drugs with different mechanisms. Your prescriber cannot simply "convert" between them — any switch requires reassessment and a new treatment plan.
How long should I stay on 5mg Mounjaro before increasing the dose?
MHRA guidance recommends staying on each dose for at least 4 weeks before escalating, to allow full effect assessment and side effect adaptation. If after 4–8 weeks on 5mg you have good tolerance but poor weight loss, your prescriber may recommend escalation to 7.5mg. Never adjust your own dose — speak to your prescriber first.
Can I use the BMI calculator and GLP-1 calculator on MyWeightCheck to understand my results better?
Yes. The free BMI calculator helps you track your current health position, whilst our GLP-1 weight loss calculator shows projected outcomes based on average trial data at different doses. These tools help contextualize your progress and support conversations with your prescriber about whether escalation is appropriate.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.